With recent proliferation in wireless services and amplification in the number of end-users, the wireless industry is fast moving toward a new wireless networking model where wireless service providers are finding it difficult to satisfy users and increase revenue with just the spectrum statically allocated. Spectrum usage being both space and time dependent, a static allocation often leads to low spectrum utilization and “artificial scarcity” of spectrum resulting in a significant amount of “white space” (unused band) available in several spectral bands that could be exploited by both licensed and unlicensed services. In order to break away from the inflexibility and inefficiencies of static spectrum allocation, the new concept of dynamic spectrum access (“DSA”) is being investigated by network and radio engineers, policy makers, and economists.
In DSA, spectrum can be opportunistically accessed dynamically by end-users in a time and space variant manner. Emerging wireless technologies such as cognitive radios, which sense the operating environment and adapt themselves to maximize performance, is anticipated to make DSA a reality.
The FCC has defined provisions that allow unlicensed devices (secondary users) to operate in the licensed bands (primary bands) opportunistically so long as the unlicensed devices avoid licensed services (primary incumbents) who are the primary owners of these bands. Thus for unlicensed devices to gain access to this opportunistic spectrum access, the FCC requires that the unlicensed devices operating on a primary band, upon arrival of a primary user(s) on this particular primary band, stop secondary communication within a certain time threshold T (the value of T may vary depending on the nature of licensed services), and switch to a new unused band.
A cognitive radio (“CR”) must periodically perform spectrum sensing and operate at any unused frequency in the licensed or unlicensed band, regardless of whether the frequency is assigned to licensed services or not. But the most important regulatory aspect is that cognitive radios must not interfere with the operation in some licensed band and must identify and avoid such bands in a timely manner. Cognitive radio enabled secondary devices operating on some primary band(s) upon detecting primary incumbents in that band(s) to automatically switch to another channel or mode within a certain time threshold. Thus accurate sensing/detection of the arrival of primary incumbents and hence the switching (moving) to some other channel are two of the most important challenging tasks in a cognitive radio network.
Cognitive radios can be viewed as electromagnetic spectrum detectors, which can find an unoccupied band and adapt the carrier to that band. The layer functionalities of cognitive radios can be separated into the physical (PHY) layer and the medium access control (MAC) layer. The physical layer includes sensing (scanning the frequency spectrum and process wideband signal), cognition (detecting the signal through energy detector), and adaptation (optimizing the frequency spectrum usage such as power, band and modulation). The medium access layer cooperates with the sensing measurement and coordinates in accessing spectrum. The requirement is that whenever cognitive radio detects primary incumbents in the currently operating channel, it must switch to some other channel within a certain time T.
Applicants propose improvements to wireless communication utilizing the information gathered and processed by the respective communication devices for spectrum selection and switching.
A wireless mesh network (WMN) is a communications network made up of radio nodes organized in a mesh topology. Wireless mesh networks often consist of mesh clients, mesh routers and gateways. The mesh clients are often laptops, cell phones and other wireless devices while the mesh routers forward traffic to and from the gateways which may, but need not, connect to the Internet. The coverage area of the radio nodes working as a single network is sometimes called a mesh cloud. Access to this mesh cloud is dependent on the radio nodes working in harmony with each other to create a radio network. A mesh network is reliable and offers redundancy. When one node can no longer operate, the rest of the nodes can still communicate with each other, directly or through one or more intermediate nodes. Wireless mesh networks can be implemented with various wireless technologies including 802.11, 802.16, cellular technologies or combinations of more than one type.
A wireless mesh network can be seen as a special type of wireless ad-hoc network. It is often assumed that all nodes in a wireless mesh network are immobile but this need not be so. The mesh routers may be highly mobile. Often the mesh routers are not limited in terms of resources compared to other nodes in the network and thus can be exploited to perform more resource intensive functions. In this way, the wireless mesh network differs from an ad-hoc network since all of these nodes are often constrained by resources.
On wireless computer networks, an ad-hoc mode can be a method for wireless devices to directly communicate with each other. Operating in an ad-hoc mode allows all wireless devices within range of each other to discover and communicate in peer-to-peer fashion without involving central access points (including, e.g., those built in to broadband wireless routers). To set up an ad-hoc wireless network, each wireless adapter must be configured for ad-hoc mode versus the alternative infrastructure mode. In addition, all wireless adapters on the ad-hoc network must use the same service set identifier (“SSID”) and the same channel number.
An ad-hoc network tends to feature a small group of devices all in very close proximity to each other. Performance suffers as the number of devices grows, and a large ad-hoc network quickly becomes difficult to manage. Ad hoc networks make sense when there is a need to build a small, all-wireless LAN quickly and spend the minimum amount of money on equipment. Ad hoc networks also work well as a temporary fallback mechanism if normally-available infrastructure mode gear (access points or routers) stop functioning, or in, e.g., addressing emergency contingencies.
Key network data linking and routing tasks are performed in a data link layer (“DLL”), such as logical link control (“LLC”), which refers to the functions required for the establishment and control of logical links between local devices on a network. This is usually considered a DLL sub-layer and provides services to a network layer above the data link layer. The data link layer LLC hides the rest of the details of the data link layer to allow different technologies to work seamlessly with the higher layers. Most local area networking technologies use the IEEE 802.2 LLC protocol. Another task is referred to as Media Access Control (“MAC”), which refers to the procedures used by devices to control access to the network medium, e.g., through a physical layer.
Since many networks use a shared medium (such as a single network cable, or a series of cables that are electrically connected into a single virtual medium, or a single wireless communications channel) it is necessary to have rules for managing the medium to avoid conflicts. For example, Ethernet uses the carrier sense multiple access with collision detection (“CSMA/CD”) method of media access control, while Token Ring uses token passing. Still another task is Data Framing, which relates to the data link layer being responsible for the final encapsulation of higher-level messages into frames that are sent over the network at the physical layer. Also accounted for is the task of addressing, wherein the data link layer is the lowest layer in the Open System Interconnection (“OSI”) model that is concerned with addressing, i.e., labeling information with a particular destination location.
Each device on a network has a unique number, usually called a hardware address or MAC address, that is used by the data link layer protocol to ensure that data intended for a specific machine gets to it properly. Finally there is the task of Error Detection and Handling, by which, the data link layer handles errors that occur at the lower levels of the network stack. For example, a cyclic redundancy check (CRC) field can be employed to allow a station receiving data to detect if the data was received correctly.
Applicants propose routing changes to the current routing technology in such networks in order to improve network performance, such as throughput.
The physical layer and data link layer are very closely related. The requirements for the physical layer of a network are often part of the data link layer definition of a particular technology. Certain physical layer hardware and encoding aspects are specified by the DLL technology being used. The best example of this is the Ethernet standard, IEEE 802.3, which specifies not just how Ethernet works at the data link layer, but also its various physical layers.
Since the data link layer and physical layer are so closely related, many types of hardware are associated with the data link layer. Network interface cards (“NICs”) typically implement a specific data link layer technology, so they are often called “Ethernet cards”, “Token Ring cards”, and so on. There are also a number of network interconnection devices that are said to “operate at layer 2”, in whole or in part, because they make decisions about what to do with data they receive by looking at data link layer frames. These devices include most bridges, switches and barters, though the latter two also encompass functions performed by layer three.
Some of the most popular technologies and protocols generally associated with layer 2 are Ethernet, Token Ring, fiber distributed data interface (“FDDI”) (plus copper distributed data interface (“CDDI”)), home phone line networking alliance (“HomePNA”), IEEE 802.11 (“wireless local area network” (“LAN”), “wireless Ethernet” or “wi-fi”), asynchronous transfer mode (“ATM”), and transmission control protocol/internet protocol (“TCP/IP's”) Serial Link Interface. The data link layer, therefore, is the place where most LAN and wireless LAN technologies are defined. Layer two is responsible for logical link control, media access control, hardware addressing, error detection and handling, and defining physical layer standards. It is often divided into the logical link control (LLC) and media access control (MAC) sub-layers, based on the IEEE 802 Project that uses that architecture.
Wireless ad-hoc and mesh networks (for example, based on IEEE 802.11 standards) are gaining prominence and play a major role in many applications. For example, during a natural disaster, a wireless mesh network for first responder communications could be established quickly. Some device constraints in a mesh network may include limited battery power and computational capabilities. In a traditional network protocol stack a data packet that is to be routed through the network experiences processing delays at every intermediate routing node. This processing delay includes computing the next best hop for the packet, re-encapsulating the packet depending on the address of the next hop, etc. Applicants have determined experimentally that, for a two hop wireless ad-hoc setup, one observes that 20% of the Round Trip Time (“RTT”) is due to these processing delays; for a three hop ad-hoc network, this is around 26% of the total RTT. At a routing node, on an average, 40% of the processing time is used to compute the next hop. Clearly, these delays result in battery power waste, data rate reductions, etc.
FIG. 19 shows a typical processing path and the system structure 100 for wired networks like the Ethernet. Here the physical layer 122 and most of the MAC layer 124 functionalities are implemented in a network interface card 120. This hardware implementation minimizes the impact due to computation induced delay and power consumption. However, this situation is different in a wireless network. FIG. 20 shows the same typical process 100′ for a wireless network protocol stack. The MAC layer 124′ in this protocol stack is very complex, prohibiting implementation in the wireless network interface card, such as 120 in FIG. 19. As a result, the wireless network interface card usually only implements the physical layer 122′ features. Most of the MAC layer 124′ features are implemented as part of a module 140 (e.g., in most cases it will be the device driver) in the operating system.
Typically, the routing layer 132 is implemented in the network layer 130. Under this structure, the routing layer 132 has three major functions. First, it maintains the routing table, including route discovery, creating a corresponding routing entry in the routing table and modifying or deleting routing entries when a route is moved, etc. Second, this layer 132 is responsible for computing the best next suitable hop for the data packet. Third, the layer 132 is responsible for re-encapsulating the data packet according to the corresponding route entry.
Applicants propose ways to address the shortcomings noted above in wireless mesh networks.
Communication devices with multiple wireless physical layer (PHY) interfaces are becoming common place. For example, smart phones can connect to a cellular network or a WiFi network using the two corresponding built-in radio interfaces. However, with current technologies a communication device equipped with multiple PHY interfaces can use only one interface to connect to one wireless network at a time. This leads to an under-utilization of radio resources such as the available spectrum from multiple networks that a device can access using its multiple PHY interfaces.
For instance, in the traditional TCP/IP protocol stack 350 as illustrated in FIG. 27, having a TCP layer 356 and an IP layer 358, a data link layer 352 may control a physical layer 354 of the device. The data link layer 352 may be divided into sub-layers: (a) a Logic Link Control sub-layer 360 and (b) a Media Access Control (MAC) sub-layer 362, as illustrated schematically and in block diagram form in FIG. 28. The MAC layer 362 may be designed so that it can control multiple physical devices. However, in a majority of the communication devices, part of the MAC layer 362 may be integrated into the hardware of the PHY layer 354. Therefore, modifying the MAC layer 362 to control multiple physical devices may require that the PHY layer 354 hardware also be modified. This may be impossible or cost prohibitive given that millions of PHY layer 354 hardware devices are manufactured and integrated into consumer communication devices.
Applicants propose improvements to the communication network to address these shortcomings.